1. Rubidium occurs naturally as a mixture of two isotopes, 72.17% Rb-85 (atomic mass 84.911 792 u) and 27.83% Rb-87 (atomic mass 86.909 186 u).
What is the average atomic mass of rubidium?
2. The element silicon occurs as a mixture of three isotopes: 92.22% Si-28, 4.69%
Si-29, and 3.09% Si-30. The atomic masses of these three isotopes are as follows:
Si-28 = 27.976 926 u, Si-29 = 28.976 495 u, and Si-30 = 29.973 770 u.
Find the average atomic mass of silicon.

Astudent made a graph plotting the progress of a reaction over time. the student forgot to label the y-axis of the graph. a graph is shown with two graph lines. one graph line starts at a higher position on the y axis and slopes downwards towards the right. the other graph line starts at a lower position on the y axis and slopes upwards towards the right. the two graph lines stop short of intersecting each other and continue as separate lines which gradually become straight and parallel to the x axis. a vertical line is shown at a point where the two graph lines finally became parallel to the x axis. this vertical line is labeled equilibrium. the title on the x axis is time and an arrow pointing towards the right is shown above time. the title on the y axis is left blank. what best explains the label that the student should use on the y-axis? amount, because as the amount of product decreases, the amount of reactant increases over time. reaction rate, because forward and backward reaction become equal at equilibrium. amount, because the amounts of reactants and products become constant after equilibrium is reached. reaction rate, as the rate of forward reaction increases and rate of backward reaction decreases over time.

One of the hopes for solving the world's energy problem is to make use of the fusion reaction 21h +31h --> 42he + 10n + energy how much energy is released when 1 mol of deuterium is fused with 1 mol of tritium according to the above reaction? the masses of the atoms and the neutrons are as follows: 21h = 2.0140 amu 31h = 3.01605 amu 42he = 4.002603 amu 10n = 1.008665 amu. the speed of light is 2.9979 x 108 m/s.

Rank the following four acids in order of increasing bronsted acidity : h2f+ , ch3oh, (ch3)2oh+ , ch3sh2+